Add timing span when emiting a timing metric (#1717)

Co-authored-by: Alex Bouma <alex@bouma.me>

src/Metrics/Metrics.php

@@ -9,6 +9,9 @@
 use Sentry\Metrics\Types\DistributionType;
 use Sentry\Metrics\Types\GaugeType;
 use Sentry\Metrics\Types\SetType;
+use Sentry\Tracing\SpanContext;
+
+use function Sentry\trace;
 
 class Metrics
 {
@@ -142,21 +145,32 @@ public function timing(
         array $tags = [],
         int $stackLevel = 0
     ) {
-        $startTimestamp = microtime(true);
-
-        $result = $callback();
-
-        $this->aggregator->add(
-            DistributionType::TYPE,
-            $key,
-            microtime(true) - $startTimestamp,
-            MetricsUnit::second(),
-            $tags,
-            (int) $startTimestamp,
-            $stackLevel
+        return trace(
+            function () use ($callback, $key, $tags, $stackLevel) {
+                $startTimestamp = microtime(true);
+
+                $result = $callback();
+
+                /**
+                 * Emitting the metric here, will attach it to the
+                 * "metric.timing" span.
+                 */
+                $this->aggregator->add(
+                    DistributionType::TYPE,
+                    $key,
+                    microtime(true) - $startTimestamp,
+                    MetricsUnit::second(),
+                    $tags,
+                    (int) $startTimestamp,
+                    $stackLevel + 4 // the `trace` helper adds 4 additional stack frames
+                );
+
+                return $result;
+            },
+            SpanContext::make()
+                ->setOp('metric.timing')
+                ->setDescription($key)
         );
-
-        return $result;
     }
 
     public function flush(): ?EventId